(a) Field of the invention
The present invention relates to an improved boom construction and to an improved tree delimbing unit incorporating such an improved boom construction.
The invention also relates to an improved hydraulic circuit assembly for use in boom construction and to an improved tree delimbing unit incorporating such an improved hydraulic circuit.
(b) Brief description of the prior art
Several types of boom constructions are well known, particularly but not exclusively, in the tree delimbing art.
A first known type of boom construction is disclosed, by way of example, in Canadian Pat. No. 1,142,062 to Jean Pelletier et al. Such a boom construction employs a hinged or knuckle boom made in two sections which are pivotally connected together, usually at adjacent ends. One end of this boom is pivotally connected to a base. Work handling means, such as tree delimbing means for example, are mounted on the other end of the boom. Hydraulic actuators are pivotally connected between the sections and hydraulic actuators are also connected between the boom and the base. Operation of the actuators hinges or unhinges the boom to move the work handling means toward or away from the base. When the hinged boom is used in a tree delimber, the work handling means at the end of the boom comprise delimbing means. Tree gripping means are provided on the base for gripping the butt end of a tree to be delimbed. To delimb a tree, the tree is first grasped by the delimbing means and the boom is manevvered to place the butt end of the tree in the gripping means. While the tree is gripped, the boom is then maneuvered to move the delimbing means along the tree to delimb it. An operator using a delimber with a hinged boom has a problem however in trying to place the butt end of a tree into the gripping means on the base. It takes a great deal of experience to properly operate the hinged boom actuating means to load the tree into the gripping means and even then the delimbing operation is slow.
Another type of boom construction known in the art is disclosed, by way of example, in Canadian Pat. No. 1,055,366 to Roger Sigouin. This other boom construction employs a straight, rigid boom that is mounted through a base. Work handling means are provided at the outer end of the boom and means are provided for sliding the boom through the base to move the work handling means toward or away from the base. When this boom is used in a tree delimber, tree delimbing means are mounted on the end of the boom and tree gripping means are mounted on the base. The delimbing operation is the same as that used with a knuckle boom except that the rigid boom slides through the base to move the work handling means. However because the boom slides through the base, it is quite easy to place the butt end of a tree to be delimbed in the gripping means on the base since the delimbing means on the boom are positioned to be aligned with the gripping means. The disadvantage of such a straight, sliding boom lies however in its moving means which usually comprises a set of chains on the boom with gears or sprockets mounted on the base. Rotation of the sprockets slides the boom relative to the base via the chains. The sprockets and chains often break however and require frequent replacement and/or maintenance thereby slowing production.
Another disadvantage of the boom constructions employing a straight, rigid, sliding boom lies in the handling of the hydraulic lines which feed and return hydraulic fluid to the work handling means located at the end of the boom. The lines carry hydraulic fluid from a supply means on the base and since the distance between the work handling means and base varies depending on the position of the boom, means must be provided to take up the slack in the lines as the work handling means moves toward the base. One common known system for handling the lines involves suspending the lines from pulleys running on support cables above the boom. As the boom moves the work handling means toward the base, the pulleys bunch together with the lines they hold looping down between adjacent pulleys. The support cables are high enough to accomodate the loops. However, the cables and loops are quite open and exposed and often suffer damage during operation, particularly when used on delimbers.